Water content in a product has been determined over decades by using a hot air oven slightly above 100.degree. C. to expel water. The product, whose water content is to be determined, is simply left in the drying oven until the product reaches an "oven dry" state where no more weight variation is obtained. The difference between the weight of the sample before drying known to those in the art as the "green" sample, and the weight after drying is equal to the weight of the water lost. Determination of what is referred to as bulk density involves the mass of the dry sample per unit volume of "green" sample.
The period of time to allow complete exhaustion of the water from a sample is determined empirically, thus permitting a sample to be dried during a known time period to insure complete water removal. This method which requires one or two days, is time consuming and does not allow rapid moisture content determination.
A more rapid determination of moisture content using a microwave oven for drying is described in Forest Products Journal 32(10) p. 56 to 58, 1982), which hereinafter is referred to as the "Journal".
The determination of the moisture content as described in the Journal, consists of placing a sample in a microwave oven, turning on the power for various intervals, and determining weight at each interval, until the sample becomes constant in weight.
With such a method, it is difficult to thoroughly dry the material without initiation of combustion. In a conventional oven, the samples reach an oven-dry state and maintain this equilibrium with continued exposure. In a microwave oven, however, extended exposure beyond the oven-dry state results in the superheating of the centre of the sample and smoldering and smoking of the wood causing unpleasant odors and degradation of material. This introduces error in the moisture content determination and a fire hazard.